1. Field of the Invention
The present invention relates to dampers and, more particularly, relates to adjustable dampers capable of providing a variable restriction of airflow through ventilation ducts.
2. Discussion of the Related Art
Ventilation in modern buildings requires that air be circulated and distributed to meet the requirements of the different parts of the building. Airflow rates are usually controlled via dampers which are adjusted either manually or automatically to vary the airflow rates through ventilation ducts. These dampers may be placed in ducts leading to individual rooms of a building or may be provided in larger ducts which supply air to east and west halves of the building. These latter dampers, when placed in air conditioning systems, are typically controlled so as to supply more cooling air to the east side of the building in the morning and to the west side in the afternoon.
The typical damper comprises a louvered device mounted to the inside of a ventilation duct. This typical device comprises a frame which is dimensioned to match the shape of the ventilation duct and in which is mounted a plurality of louvers or slats which extend transversely across the ventilation duct. These slats are rotatable about the frame from positions permitting substantially free flow of air through the damper to positions blocking all or nearly all of the air flowing through the damper. The louvers or slats are typically adjusted manually via a lever or automatically via an electrical, hydraulic, or pneumatic motor.
Louvered dampers of the type discussed above exhibit several disadvantages. The individual slats or louvers must be connected to a common linkage but at the same time must be individually rotatable with respect to the frame. This results in a relatively complex structure which is difficult and expensive to assemble and which requires frequent maintenance. Jamming often occurs because of the buildup of dust or corrosion between the slats and the frame.
Louvered dampers may also vibrate when air is flowing through the duct, or produce an unpleasant whistling noise as air rushes between adjacent slats. Such dampers are also difficult to install in ventilation ducts because their frames engage the entire circumference of the associated ducts. As a result, all or substantially all of a cross section of a duct must be accessible when the damper is mounted in the duct. Retrofitting dampers in existing ducts is therefore difficult, if not impossible.
In addition, louvered dampers having rigid frames are either not adjustable or can be adjusted only within narrow limits. Accordingly, such dampers must be designed with relatively close tolerances to closely match the shape of the ventilation ducts in which they are to be installed. A square duct thus requires a square damper, a round duct requires a round damper, etc. As a result, retailers must carry a wide variety of dampers to match the demands of a particular application and must custom build dampers to match other applications.